Conversion of ethylene oxide to valuable products



April 28, 1953 H. s. DAvls 2,636,906

CONVERSION OF' ETHYLENE OXIDE TO VALUABLE PRODUCTS Filed March 5, 1948ETHYLE'NE GLYCOL INVENTOR.

H/l 5. DHV/5;

C'a Clt? Patented Apr. 28, 1953 CONVERSION OF ETHYLENE OXIDE' TOVALUABLE PRODUCTS.

Harold Si.. Davis, Riverside', Conn., assigner toy American- CyanamidCompany, New York, Y.,

acorporation. of Maine Application March 5, 1948', Serial No. 13,117

i clame. (c1. 26oessiy This invention relates to the preparation ofvaluable products using ethylene oxid'e and pref-- erably the diluteethylene oxidel in the gases which result from the direct oxidation oi"ethylene by oxygen containing gases in the presence of a catalyst. Atypical gas from this operation con'- tains, in percentages by volume,ethylene oxide 2.2%, carbon dioxide 3.6%, ethylene 0.9%, the remainderbeing largely' nitrogen with some water vapor.

@ne obiec't of the invention is to absorb ethylene oxide selectively andcompletely from. a gas mixture containing it, leaving the othercompounds, particularlyI carbon dioxide and ethylene, substantiallyuntouched. It is then possible to obtain more value from the ethylene.inthe gas; from which ethylene oxide has been removed e. g. by recyclingthe gas, after proper additions, in the direct oxidation procedure, orthe ethylene can be separated from the. gas by known art in a moreconcentrated and' useful form.

Another object oi the invention is the simultaneous production of morethan one valuable product from ethylene oxide in very high yield on thetotal ethylene oxide consumed.

Another object of the invention is the production of a neutral productsolution, free from dissolved salts, Which can be distilled Withoutcorrosive tendencies and Without the deposition of solid salts in theapparatus during the distillation.

Another object of the invention is the production or" high gradeethylene glycol.

Another object of the invention is the production from a dilute ethyleneoxide gas mixture oi a high grade or concentrated ethylene oxide throughan aqueous solution of ethylene chlorohydrin by' heating with milk of'lime according to known art.

Another object of the invention is a simple method forutilizing free.hydrochloric acid in` the aqueous solution of ethylene chlorohydrinwhich results from the reaction of. ethylene with a dilute solution ofchlorine and' whichv aqueous solution is the main primary product in thecommercial process for manufacturing ethylene chlorohydrin fromethylene.

These objects are accomplished by scrubbing ethylene oxide or gases.containing it with aqueous hydrochloric acid. The ethylene oxide israpidly and selectively absorbed by the solution and re'- acts With itto give glycol and ethylene chlorohydrin practically quantitatively.

Preferably the absorbing solution is maintained in contact withethyl-ene oxide until the solu tion becomes neutral. The ethylenechloro- 2. hydriri. and: glycol in the solution are then separated. Thismaybe accomplished by distillation and it has been found' that all theethylene. chlorohydrin tends to come over in the 'hrst part oi thedistillate as an azeotrope with water at SlT-98 C., then the remainderof the Water dis- Gillsy overv and all the glycol remains behind. Thedistillate of ethylene chlorohydrin and Water, particularly the firstpart which is rich in chlorohydrin, is very suitable for making pureethylene oxide by heating it' with milk of' lime. Therefore, iin eiiect,WhileY making glycol from party of. the dilute ethylene oxide, all theremainder is recovered as purev concentrated ethylene` oxide.Hi-therto',A no satisfactory methodr for doing vthis has'v beendeveloped and commentators on ex'- tensive German practice actuallystate that it appearsimpossible4 to recover pure ethylene oxide directlyin industrial scale from the gas stream.

Hitlaerto, the most successful method for utilizing dilute ethyleneyoxide has been by scrubbing the gases with an aqueous solutioncontaining dilute sulfuric acid. The ethylene oxide is rapidly' absorbedand ethylene glycol with some polyglycol is' produced. Apart from thefact that it gives only glycol, this method has the serious disadvantagethat the primary' product solution is acidic; Before distil'ling torecover pure glycol, it is necessary' to neutralize all the sulfuricacid with, for instance, caustic soda. The resulting sodium sulfateprecipitates out gradually as distillation proceeds. and greatlycomplicates the operations.

It has now been found that ethylene oxide reacts equally fast withdilute hydrochloric acid,

two; overall' reactions takingA place simultaneously.

(A), Chlorohydrin formation` C2H40+HC1 ClC2H4 (Oflrlll (Bl Glycolformation C2i-140 +E2O- (HO) 62H4 (OH) If sufficient ethylene oxide issupplied and if the rapid reactions are. allowed to run to completi'on',then all the free HC1 is used up and the product is a neutral solutionof ethylene glycol and ethylene chlorohydrin. This could not have beenforeseen. Nor could. it have been foreseen that the ethylene. glycol,and ethylene chlorohydrin in an aqueous solution of the two could beeasily and completely segregated by dis tillation, that is to say thatthere is no ternary azeotrope ofthe three components.

Reference is here made to the iiovvv sheetl in they drawing whichillustrates a preferred manner of practising the invention.

solution of ethylene chlorohydrin, HC1 and perhaps some ethylene glycol.The liquid in the reactor acts to scrub out the ethylene oxide whichreacts with the hydrochloric acid to form ethylene chlorohydrin. Due tothe fact that there is a considerable quantity of water present,ethylene glycol also forms. The reaction may continue until all of thehydrochloric acid is used up, at which time the contents of the reactorwill be neutral. It is 'preferable to carry out the absorption of theethylene oxide in two stages. In the rst where the main absorption takesplace, free hydrochloric acid is maintained in the absorbing liquid inorder to promote the reactions. In the second, the still acid solutionfrom the first stage is contacted with ethylene oxide, preferablycountercurrently, until it becomes neutral. The reaction products arefractionally distilled, an azeotrope of ethylene chlorohydrin and watercoming over rst. This is then followed by water containing little or noethylene chlorohydrin while the ethylene glycol produced remains in thestill and may be recovered as such.

The ethylene chlorohydrin and water taken from the still may then bepassed to a reactor and lime or milk of lime added to form ethyleneoxide and calcium chloride. The ethylene oxide may then be returned tothe cycle or recovered as a concentrated gas and used for any purpose.The calcium chloride may be recovered or disposed of as desired.

The reaction of ethylene oxide with hydrochloric acid is very fast butby no means instantaneous. This can be shown easily by adding definitequantities of concentrated hydrochloric acid to aqueous solutions ofethylene oxide in a Dewar flask and observing the rise in temperaturewith time in the reacting mixture. The rate of reaction increasesrapidly with the temperature. Indeed if too much of the reactants isused, the solution may suddenly rise to boilin temperature in a fewseconds.

Calculations indicate that the heats involved by the reactions are about20,200 calories per gram mole of glycol and 11,900 calories per grammole of chlorohydrin, and the order o f these values has been confirmedby calorimetric measurements. Since sulfuric acid directs the reactionof ethylene oxide to glycol, it might have been expected that sulfuricacid would absorb ethylene oxide somewhat faster than hydrochloric.Nevertheless, tests with normal solutions of the two acids failed todisclose any difference in the rates of the reactions except that theone with HCl started at once whereas there was always a short lag orinduction period before the one with H2504 got under way.

The quantity of glycol relative to chlorohydrin which is produceddepends upon the concentration at which the HC1 is maintained in theabsorbing solution. The lower this concentration and the higher thetemperature, the greater will be the proportion of glycol. If a highconcentration of HC1 is maintained, then chlorohydrin,A

is the main product. Indeed glycol formation can be suppressedpractically entirely by maintaining a high concentration of chloride ioneither by free hydrochloric acid alone or by a combination of HCl andany soluble metallic chloride, preferably the soluble chlorides of thealkali forming metals such as NaCl, CaClz or MgCl2. In this last case,absorption of the ethylene oxide and distillation of the aqueouschlorohydrin may be carried out in successive operations. Or, the twooperations may be carried out concurrently and continuously, bymaintaining the absorbing solution at a moderately elevated temperaturewhere the unabsorbed gases carry out from the solution both water at thesame rate at it is added and chlorohydrin at the same rate as it isproduced. The chlorohydrin may then be recovered from the gases bycooling in the form of an aqueous solution.

Very valuable results can be obtained through the invention by combiningthe process of the hypochlorination of ethylene with that of the directoxidation. In the former process, ethylene is contacted with a dilutesolution of chlorine in water and reacts mainly according to theequation:

In practice, the primary effluent is a water solution containing about5% ethylene chlorohydrin and free hydrochloric acid in chemicalequivalence thereto. It is customary to treat this eluent with limewhereupon ethylene oxide is produced and waste calcium chloride isformed according to the equation:

In accordance with this invention, this primary eiiluent can be used toabsorb the dilute ethylene oxide out of the product gases from thedirect oxidation of ethylene whereupon reaction takes place according tothe equation:

I Hence the 4free HCl is used up to form an equivalent quantity ofchlorohydrin. The chlorohydrin is then separated by distillation in theform of an azeotrope with water and may be used to make ethylene oxideby heating with milk of lime. Thus, compared to the hypochlorinationprocedure above, there results twice the quantity of ethylene oxide fromthe same quantities of chlorine and lime. It is also of great practicalimportance that there is only half the quantity of waste CaClz per unitof ethylene oxide. In effect, the extra ethylene oxide has beenrecovered from the dilute ethylene oxide in the direct oxidation gases.In addition, the residue from the distillation of the aqueouschlorohydrin may be high grade glycol free from dissolved salts. It toocan be formed by hydrolysis of dilute ethylene oxide from the directoxidation gases. The proportion glycol/chlorohydrin depends upon theconditions of chloride ion concentration and the temperature used in theabsorption of the dilute ethylene oxide.

Example 1 vA mixture of 10 g. of ethylene glycol, l0 g. of ethylenechlorohydrin and g. of Water was distilled through an ecientfractionating column. The first 31 g. of distillate contained 80% of thechlorohydrin, the next 51 g. contained 18% and the next 8 g. were purewater. There remained in the distilling ask 9.6 g. of glycol having thesame refractive index as the original sample, 1,4310.

Example 2 A similar mixture to that used in Example 1 was rapidlydistilled through a short, unpacked, relatively' ineiilcient column. Thefirst 50.7 of distillate contained 88% of the chlorohydrin and 3% wasfound in the next 38.5 g. The remaining 9% undoubtedly representsmechanical loss. 92% of the glycol, refractive index 1.4309, remained inthe flask.

Example 3 Ethylene oxide was passed into 100 g. of 0.93 N (3.5%) HC1 atabout 50 C. It Was rapidly absorbed with evolution of heat which wasremoved by cooling. The solution soon became neutral and 15.5 g. ofethylene oxide had been absorbed. The solution was now reuxed under anice cooled, low temperature column and 4.3 g. of unreacted ethyleneoxide came over at lil-11 C. The solution was then distilled andanalyzed according to the procedure in Example 2. Ethylene chlorohydrinwas found in the distillate in 93% equivalence to the HC1 taken. Thisrepresents quantitative chlorohydrin formation. 10.2 g. of ethyleneglycol Were recovered. Its refractive index was 1.4298 and whendistilled 9.1001113 80% boiled at ISB-200 C, The

flask Went to dryness at 208 C. but higher boiling material, presumablypolyethylene glycols were still refluxing.

Example 4 In order to find the effect of the HCl concentration, testswere carried out at in a manner similar' to Example 3. To show theeffect of temperature, the results from Example 3 are included. Thedilute acid in test C represents the addition of 10 cc. of concentratedHC1 in 1 cc. portions over 45 minutes to 90 g. of Water into whichethylene oxide Was being passed.

The ratio glycol/chlorohydrin increases with the dilution of the HCl andis somewhat higher at 50 C. than at 20 C.

The glycol from tests B and C was purer than that in Example 3. Most ofit distilled at 19T-198 C. and the refractive index of this distillatewas 1.4310 at C.

Example 5 Ethylene oxide was passed into a solution containing MgClz and4.2% HC1 until the solu- 6 tion became neutral. After removing unreactedethylene oxide, 43 g. of distillate were taken over and analyzed.

Ethylene oxide reacted 0.132 eq. Ethylene chlorohydrin in distillate0.132 eq. HC1 taken 0.114 eq.

All the reacted ethylene oxide can be accounted for as ethylenechlorohydrin. Accordingly glycol formation must have been negligible.

There Was more chlorohydrin than corresponded to the HC1 taken.Presumably the extra HC1 came from hydrolysis of the MgCl2.

While the invention has been described with particular reference tospecific embodiments, it is to be understood that it is not to belimited thereto but is to be construed broadly and restricted solely bythe scope of the appended claims.

I claim:

1. The method which includes passing ethylene oxide into an aqueoussolution of hydrochloric acid until a neutral solution of ethylenechlorohydrin and ethylene glycol is formed and thereafter removingethylene chlorohydrin by distillation.

2. A cyclic method of making ethylene glycol which includes passingethylene oxide into an aqueous solution of hydrochloric acid to form aneutral solution of ethylene chlorohydrin and ethylene glycol,distilling ethylene chlorohydrin from the reaction mixture andrecovering ethylene glycol from the residue, reacting ethylenechlorohydrin with milk of lime to form ethylene oxide and returning thelatter to the cycle.

3. The method which includes passing ethylene oxide into an aqueoushydrochloric acid until a neutral solution of ethylene chlorohydrin andethylene glycol is formed.

4. The method of claim 1 in which the aqueous solution of hydrochloricacid contains a Water soluble metallic chloride.

HAROLD S. DAVIS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,954,395 Stampe Apr. 10, 1934 2,103,849 Heard Dec. 28, 19372,188,254 Smithuysen Jan. 23, 1940 2,255,411 Cohen et al Sept. 9, 19412,325,576 Balear July 27, 1943 2,378,104 Reed June 12, 1945 OTHERREFERENCES Chemical and Metallurgical Engineering, vol. 22, pp. 629-30(1920) (Brooks).

Journal of the Society of Chemical Industry, Japan, vol. 38, p. 425(1935).

Journal of the American Chemical Society, vol. 51 (1929), pp. 428, 429,440, 457, 460 and 461 (Bronsted et al.)

Jour. Am. Chem. Soc., vol. 56, p. 2009 (1934)l (Gebauer-Fuelnegg andMoffett)

3. THE METHOD WHICH INCLUDES PASSING ETHYLENE OXIDE INTO AN AQUEOUSHYDROCHLORIC ACID UNTIL A NEUTRAL SOLUTION OF ETHYLENE CHLOROHYDRIN ANDETHYLENE GLYCOL IS FORMED.